Question

How do you calculate the molar mass of a gas?

Answer 1

In order to know how to calculate molar mass of a gas, we must first know what a molar mass is. We must always remember that Molar mass is different from the Molecular mass. Molar mass is also called the Molecular weight. Molar mass of the chemical compound is the mass of one mole of the compound.

Complete answer:
First let us understand, what is a Molar mass? Molar mass, also called as the Molecular weight, is the mass of one mole of the substance. It is expressed in the units of g/mol. Molar mass is different from the Molecular mass.
Molar mass of the gas can be derived by using the ideal gas equation.
The ideal gas equation is given as
${\text{PV = nRT}}$…… (1)
Where n is the number of moles of the gas.
We can give the molar mass as
${\text{M = }}\dfrac{m}{n}$
Where m is the mass of gas and n is the number of moles of gas.
Substitute the value of n in the equation (1).
i.e., $n = \dfrac{m}{M}$
$PV = \dfrac{{mRT}}{M}$
$M = \dfrac{{mRT}}{{PV}}$
Therefore, the molar mass of the gas can be obtained by the formula:
$M = \dfrac{{mRT}}{{PV}}$

Note:
Comparison between molar mass and Molecular mass are given below:

MOLAR MASS	MOLECULAR MASS
Molar mass is the mass of one mole of the substance.	Molecular mass is the mass of the molecule.
It is expressed in g/mol.	It is expressed in amu.
It is also known as Molecular weight.	It determines the mass of a single molecule.